Adult Hip Dysplasia

Adult hip dysplasia is acetabular underdevelopment carried over from infancy or childhood: the socket never grew to cover the head, and the result is progressive instability and premature osteoarthritis. It is often undiagnosed in infancy and declares itself in early adulthood, once it becomes painful.

Why it matters. DDH is the leading cause of hip arthritis in women under 40, and about 10% of total hip arthritis in young adults is dysplastic in origin. Recognised early, the hip can be preserved with a periacetabular osteotomy before the cartilage damage becomes irreversible; missed, it ends in arthroplasty in the third or fourth decade, with the high revision burden that an early THA carries.

Who. Women outnumber men 9:1, due to hormonal laxity, and the painful subluxation presents at 20-40 years. Prevalence is higher in First Nations and Southern European populations. The contralateral hip is dysplastic in 20-30%, so the radiograph is always of the whole pelvis and never of the symptomatic side alone; when both hips need a PAO, the operations may be staged 6-12 months apart.

Natural history. Left untreated, 50-75% have developed arthritis by the age of 50, and the functional limitation is already significant in the third decade.

The cascade. A shallow acetabulum concentrates load on a smaller area of cartilage. Contact stress rises, the rim is overloaded, the labrum tears, cartilage is lost progressively and arthritis arrives early. The lateral centre-edge angle is the measure of that coverage, and once it falls under 25° the contact stress on the remaining cartilage doubles.

The labrum. Anterosuperior labral tears are present in 90% of symptomatic dysplastic hips. Chronic edge loading makes the labrum hypertrophic, it degenerates within its substance, and in long-standing disease it ossifies.

The capsule. Capsular laxity contributes to the instability and the capsule becomes redundant in chronic subluxation; in the Crowe IV hip it is adherent within the false acetabulum. The ligamentum teres is hypertrophic.

Three systems answer three different questions. Crowe describes how far the femoral head has migrated, Hartofilakidis describes what has become of the acetabulum, and Tönnis grades the arthritis that decides whether the joint can still be preserved.

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History. The complaint is groin pain, anterior or anterolateral, worse with activity. Clicking or catching points to labral pathology, and a sensation of subluxation or giving way to instability. Ask about hip screening, bracing or surgery in childhood, and about DDH in relatives, because there is a genetic component.

Gait and length. Watch the patient walk before anything else. A Trendelenburg gait, the trunk shifting over the stance leg because the abductors are insufficient, is the finding to look for, and the Trendelenburg test (the pelvis drops on the opposite side) is positive in 40-60% of symptomatic DDH; abductor strength is often weak from the disturbed lever arm. In high dislocation the limb is apparently short from pelvic tilt, so measure both true length (ASIS to medial malleolus) and apparent length (umbilicus to malleolus).

Movement. Range is usually preserved early (flexion normally 120° or more, abduction 45°, adduction 30°) and falls as arthritis develops; loss of internal rotation is often the first sign of arthritis. Document the range, because it feeds the PAO-versus-THA decision.

Provocative tests. The FADIR test (flexion-adduction-internal rotation) reproduces anterior pain from impingement or an anterosuperior labral tear; the FABER test (flexion-abduction-external rotation) looks for posterior impingement or the sacroiliac joint. Apprehension or a clunk in flexion-abduction-external rotation is the sign of instability.

Differential Diagnosis of the Painful Young Adult Hip

Radiographs. The first study is a weight-bearing AP pelvis with the coccyx centred over the pubic symphysis. On it measure the lateral centre-edge angle and the Tönnis angle and grade the arthritis; a false profile view adds the anterior centre-edge angle, and an anterior CEA under 20° is anterior deficiency. The thresholds are in the table below.

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CT. A 3D CT of the pelvis is the planning study for PAO or THA. It gives acetabular version, the bony defects and, in Crowe III-IV, the location of the true acetabulum, and it allows templating and virtual correction.

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MRI arthrogram. The gold standard for labral pathology, with a sensitivity over 90% for tears. It also grades the cartilage (Outerbridge), which is what decides PAO candidacy or the need for arthroscopy.

Diagnostic arthroscopy. In the equivocal PAO candidate, arthroscopy looks at the cartilage directly: Outerbridge grade 3-4 change means a poor PAO candidate. A labral tear can be addressed at the time of PAO, staged or simultaneous.

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Algorithm

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The decision turns on two things: the state of the cartilage and the age of the patient. Preserve the joint while the cartilage allows it; replace it, anatomically, when it does not.

Non-Operative ManagementPeriacetabular Osteotomy (PAO)Total Hip Arthroplasty

Initial Conservative Approach

Who. Patients who are asymptomatic or mildly symptomatic, the borderline hip with a CEA of 20-25°, and older patients who decline surgery.

Conservative Treatment Steps

ImmediateActivity Modification

Avoid high-impact activity (running, jumping). Swimming and cycling maintain fitness without excessive loading. Weight management is critical.

6-12 weeksPhysiotherapy

Strengthen the hip abductors (gluteus medius) to compensate for the biomechanical disadvantage, with core stability and pelvic control, and stretch the hip flexors and iliotibial band.

OngoingAnalgesia

NSAIDs for symptom control, avoiding chronic use, and paracetamol for baseline pain. An intra-articular steroid injection gives temporary relief and confirms an intra-articular source.

AnnualSurveillance

Annual radiographs to monitor progression.

When it has failed. Surgery is indicated when pain limits function despite therapy, when the radiographs show progression with loss of joint space or the symptoms worsen, or when the patient wants definitive treatment before the damage becomes irreversible.

Bernese Periacetabular Osteotomy

The operation. The Bernese PAO is the gold standard for joint preservation in symptomatic dysplasia with preserved cartilage. Several cuts around the acetabulum free it without disrupting the posterior column, so the fragment can be reoriented to increase lateral and anterior coverage while the hip stays congruent.

Indications

• Lateral CEA under 25° with symptoms
• Age under 40-45 years
• Tönnis grade 0-1 (minimal arthritis)
• Joint space over 2mm
• Failed conservative management

Contraindications

• Advanced arthritis, Tönnis grade 2-3
• Joint space under 2mm
• Extensive cartilage loss on MRI or at arthroscopy (Outerbridge grade 3-4 changes, diffuse loss)
• Large osteophytes, which suggest irreversible degeneration
• Stiffness, which indicates advanced disease
• Age over 45 (relative): THA is likely within 10-15 years anyway
• A Tönnis angle under 0°, which is overcoverage or pincer: consider rim trimming instead
• Excessive retroversion, which may need additional femoral correction

The age contraindication is genuinely relative, and the numbers show why cartilage outranks the birth date. In 166 patients aged 40 or older (mean 44, median follow-up 9.6 years), median hip survival tracked the Tönnis grade rather than the age: 17.0 years for grade 0, 14.6 years for grade 1, and 12.9 years for grade 2. Higher preoperative Tönnis grade and worse baseline WOMAC function predicted failure; age alone did not disqualify. So a 46-year-old with Tönnis 0 disease and good function is a better PAO candidate than a 38-year-old with Tönnis 2 — and the 30-year Bern series agrees, giving preoperative Tönnis grade over 1 a hazard ratio of 5.7 against 4.3 for age over 40.

Read the grade-2 figure carefully before using it as permission, though: 12.9 years of median survival is not nothing, but Tönnis 2 remains listed above as a contraindication because those hips are also the ones most likely to be made worse by an osteotomy that does not address established cartilage loss. Evidence is Level IV retrospective, from dedicated hip-preservation centres.

What it offers, and what it costs. It restores normal biomechanics and preserves the native joint, delaying or preventing THA for 10-20 years or more, and it can allow pregnancy and high activity. Against that, it is complex surgery with a steep learning curve and a long recovery, the complication rate is 10-15% (nerve injury, nonunion), it cannot be reversed if arthritis progresses, and a THA may still be needed eventually.

Don't Forget the Femur — Combined Version and Femoral Correction

Dysplasia is a bipolar problem: the femur is frequently abnormal too, and an acetabular-only plan can fail if the femoral side is ignored. Always assess femoral version on CT/MRI (normal roughly 10-20°): excessive anteversion adds anterior instability and a positive apprehension sign, whereas relative femoral retroversion drives anterior impingement. The McKibbin (combined) index — acetabular version plus femoral version — captures the total picture: a very high combined value indicates gross anterior instability, a very low or negative value indicates impingement. When femoral version is grossly abnormal (broadly, anteversion more than about 35°, or frank retroversion), a femoral derotational osteotomy can be combined with the PAO; a non-spherical or incongruent head, or marked coxa valga, may need a varus or reorientation proximal femoral osteotomy to restore congruency. The corollary trap: a PAO that over-anteverts the socket on top of an already anteverted femur worsens anterior instability — plan the two sides together rather than treating the acetabulum in isolation.

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THA for DDH

Who. Age over 40-50, Tönnis grade 2-3 arthritis, or a failed PAO.

THA Planning Steps

EssentialPreoperative Templating

3D CT templating for Crowe II-IV. Identify the true acetabulum, plan femoral shortening if needed, template cup size and position, and assess the bone stock for grafting needs.

CriticalImplant Selection

An uncemented acetabular component if bone stock is adequate, with trabecular metal considered for defects. Small femoral stems are often required, and modular necks may aid version correction.

Surgeon PreferenceApproach Selection

The posterior approach is the most common; anterolateral if the abductors are already weak. A trochanteric osteotomy is an option if femoral shortening is required, and heals better than a subtrochanteric cut.

IntraoperativeNeurovascular Monitoring

SSEP/MEP monitoring for Crowe III-IV cases, with intraoperative nerve stimulation if lengthening exceeds 3cm.

The 4cm Lengthening Rule

Sciatic nerve palsy risk increases dramatically with lengthening over 4cm. For Crowe III-IV hips, perform subtrochanteric or trochanteric shortening osteotomy to allow anatomic cup placement without excessive lengthening.

PAO Outcomes

What predicts PAO failure. A Tönnis grade of 2 or higher at the time of surgery. A joint space under 2mm, age over 40 and inadequate correction (a final CEA under 25°) also predict a poor outcome.

THA Outcomes in DDH

What helps and what hurts. THA does best in the Crowe I-II hip with an anatomic cup, adequate bone stock, modern implants (highly cross-linked polyethylene) and properly restored leg length. It does worse in Crowe III-IV, with a high hip centre, in patients under 50, with poor bone quality, and when a femoral shortening osteotomy has added its complexity.

Registry signal. Across the major national joint registries, THA performed for developmental dysplasia carries a higher long-term revision burden than THA for primary osteoarthritis, driven mainly by younger age at surgery, severe (Crowe III-IV) dysplasia, a high hip centre and acetabular bone deficiency. Restoring the anatomic centre of rotation, securing durable acetabular fixation and using modern bearings are the principal modifiable factors.

Joint-preservation survivorship at a glance